1/*- 2 * Copyright (c) 2006 nCircle Network Security, Inc. 3 * Copyright (c) 2009 Robert N. M. Watson 4 * All rights reserved. 5 * 6 * This software was developed by Robert N. M. Watson for the TrustedBSD 7 * Project under contract to nCircle Network Security, Inc. 8 * 9 * Redistribution and use in source and binary forms, with or without 10 * modification, are permitted provided that the following conditions 11 * are met: 12 * 1. Redistributions of source code must retain the above copyright 13 * notice, this list of conditions and the following disclaimer. 14 * 2. Redistributions in binary form must reproduce the above copyright 15 * notice, this list of conditions and the following disclaimer in the 16 * documentation and/or other materials provided with the distribution. 17 * 18 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 19 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR, NCIRCLE NETWORK SECURITY, 22 * INC., OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 23 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED 24 * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR 25 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF 26 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING 27 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS 28 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 29 */ 30 31#include <sys/cdefs.h> 32__FBSDID("$FreeBSD: stable/11/sys/kern/kern_priv.c 339446 2018-10-20 16:20:36Z jamie $"); 33 34#include <sys/param.h> 35#include <sys/jail.h> 36#include <sys/kernel.h> 37#include <sys/priv.h> 38#include <sys/proc.h> 39#include <sys/sdt.h> 40#include <sys/sysctl.h> 41#include <sys/systm.h> 42 43#include <security/mac/mac_framework.h> 44 45/* 46 * `suser_enabled' (which can be set by the security.bsd.suser_enabled 47 * sysctl) determines whether the system 'super-user' policy is in effect. If 48 * it is nonzero, an effective uid of 0 connotes special privilege, 49 * overriding many mandatory and discretionary protections. If it is zero, 50 * uid 0 is offered no special privilege in the kernel security policy. 51 * Setting it to zero may seriously impact the functionality of many existing 52 * userland programs, and should not be done without careful consideration of 53 * the consequences. 54 */ 55static int suser_enabled = 1; 56SYSCTL_INT(_security_bsd, OID_AUTO, suser_enabled, CTLFLAG_RWTUN, 57 &suser_enabled, 0, "processes with uid 0 have privilege"); 58 59static int unprivileged_mlock = 1; 60SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_mlock, CTLFLAG_RWTUN, 61 &unprivileged_mlock, 0, "Allow non-root users to call mlock(2)"); 62 63static int unprivileged_read_msgbuf = 1; 64SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_read_msgbuf, 65 CTLFLAG_RW, &unprivileged_read_msgbuf, 0, 66 "Unprivileged processes may read the kernel message buffer"); 67 68SDT_PROVIDER_DEFINE(priv); 69SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__ok, "int"); 70SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__err, "int"); 71 72/* 73 * Check a credential for privilege. Lots of good reasons to deny privilege; 74 * only a few to grant it. 75 */ 76int 77priv_check_cred(struct ucred *cred, int priv, int flags) 78{ 79 int error; 80 81 KASSERT(PRIV_VALID(priv), ("priv_check_cred: invalid privilege %d", 82 priv)); 83 84 /* 85 * We first evaluate policies that may deny the granting of 86 * privilege unilaterally. 87 */ 88#ifdef MAC 89 error = mac_priv_check(cred, priv); 90 if (error) 91 goto out; 92#endif 93 94 /* 95 * Jail policy will restrict certain privileges that may otherwise be 96 * be granted. 97 */ 98 error = prison_priv_check(cred, priv); 99 if (error) 100 goto out; 101 102 if (unprivileged_mlock) { 103 /* 104 * Allow unprivileged users to call mlock(2)/munlock(2) and 105 * mlockall(2)/munlockall(2). 106 */ 107 switch (priv) { 108 case PRIV_VM_MLOCK: 109 case PRIV_VM_MUNLOCK: 110 error = 0; 111 goto out; 112 } 113 } 114 115 if (unprivileged_read_msgbuf) { 116 /* 117 * Allow an unprivileged user to read the kernel message 118 * buffer. 119 */ 120 if (priv == PRIV_MSGBUF) { 121 error = 0; 122 goto out; 123 } 124 } 125 126 /* 127 * Having determined if privilege is restricted by various policies, 128 * now determine if privilege is granted. At this point, any policy 129 * may grant privilege. For now, we allow short-circuit boolean 130 * evaluation, so may not call all policies. Perhaps we should. 131 * 132 * Superuser policy grants privilege based on the effective (or in 133 * the case of specific privileges, real) uid being 0. We allow the 134 * superuser policy to be globally disabled, although this is 135 * currenty of limited utility. 136 */ 137 if (suser_enabled) { 138 switch (priv) { 139 case PRIV_MAXFILES: 140 case PRIV_MAXPROC: 141 case PRIV_PROC_LIMIT: 142 if (cred->cr_ruid == 0) { 143 error = 0; 144 goto out; 145 } 146 break; 147 default: 148 if (cred->cr_uid == 0) { 149 error = 0; 150 goto out; 151 } 152 break; 153 } 154 } 155 156 /* 157 * Writes to kernel/physical memory are a typical root-only operation, 158 * but non-root users are expected to be able to read it (provided they 159 * have permission to access /dev/[k]mem). 160 */ 161 if (priv == PRIV_KMEM_READ) { 162 error = 0; 163 goto out; 164 } 165 166 /* 167 * Now check with MAC, if enabled, to see if a policy module grants 168 * privilege. 169 */ 170#ifdef MAC 171 if (mac_priv_grant(cred, priv) == 0) { 172 error = 0; 173 goto out; 174 } 175#endif 176 177 /* 178 * The default is deny, so if no policies have granted it, reject 179 * with a privilege error here. 180 */ 181 error = EPERM; 182out: 183 if (error) 184 SDT_PROBE1(priv, kernel, priv_check, priv__err, priv); 185 else 186 SDT_PROBE1(priv, kernel, priv_check, priv__ok, priv); 187 return (error); 188} 189 190int 191priv_check(struct thread *td, int priv) 192{ 193 194 KASSERT(td == curthread, ("priv_check: td != curthread")); 195 196 return (priv_check_cred(td->td_ucred, priv, 0)); 197} 198